Atomic (or molecular) beams, which have now become standard laboratory tools, play very important roles in the field of atomic, molecular and optical physics. These beams have been widely used in the determination of atomic structures [1]}, measurement of physical constants [2]}, studies of chemical reactions [3]} and atomic frequency standards [4]}. In all these applications, measurement of the velocity distribution of the atomic beams is both necessary and highly important. Many spectroscopic techniques have been developed to perform these measurements [5]}, [6]}, [7]}, [8]}, [9]}, [10]}, [11]}, [12]}. However, the precise determination of the velocity distribution of an atomic beam, and especially that of a well collimated atomic beam, remains challenging because of the low signal-to-noise ratio and relatively low spectroscopy resolution of these beams.
